Development and Evaluation of the Conjunctive Surface‐Subsurface Process Model Version 3 (CSSPv3) at Global Scale

Abstract The global terrestrial water and carbon cycles have evolved rapidly during recent decades, particularly in regions with intensive anthropogenic interventions and vulnerable ecohydrological systems. However, current land surface models (LSMs) and global hydrological models (GHMs) often treat natural ecohydrological processes and human water use in isolation, leaving a critical gap in the holistic understanding of coupled human‐natural systems at global scale. To bridge this gap, we developed the Conjunctive Surface–Subsurface Process Model version 3 (CSSPv3), a global land surface‐ecology‐hydrology coupled model that innovatively integrates human activities including irrigation and reservoir operation, dynamic water‐carbon couplings, and glacier freeze–thaw cycles within a water–energy balanced framework. A global offline simulation for 1991–2020 using CSSPv3 with a spatial resolution of 0.25° is validated against extensive observations, demonstrating that CSSPv3 outperforms its predecessor, CSSPv2, particularly for simulations of streamflow over human and glacier influenced basins, and evapotranspiration over irrigation fields. Moreover, the CSSPv3‐generated global water product demonstrates advantages for representing irrigation amount, streamflow, surface soil moisture, evapotranspiration, and glacier mass change as compared with 26 global products. The CSSPv3‐generated global carbon product is consistent with global ensemble medians from other products. These results establish CSSPv3 as a robust and comprehensive platform for simulating coupled ecohydrological processes under both natural climate variability and human influence, providing a powerful tool for advancing land surface modeling in the Anthropocene.